dx1/dt=p1*x4 - p4*x1;
dx2/dt=p5*x1 - p6*x2;
dx3/dt=p7*x2 - p8*x3;
dx4/dt=-p3*x3^(p3 - 1)*x4^2*(p7*x2 - p8*x3);
y1=x1;
y2=x2;
y3=x3;
x1(0)=0.3;
x2(0)=0.9;
x3(0)=1.3;


